1. Technical Field
The present technology relates to a run flat tire, and particularly relates to a run flat tire configured so as to have both durability when run-flat traveling and riding comfort when regular traveling.
2. Related Art
Generally, in run flat tires provided with a side reinforcing layer having a falcated cross-section on an inner surface side of a side wall portion, methods such as increasing a thickness of the side reinforcing layer and using a rubber with a high hardness have been used in order to ensure durability when run-flat traveling. However, when only these sorts of technologies are applied, there are problems in that the degree to which excellent run flat durability can be ensured is limited and riding comfort when regular traveling is significantly worsened due to an increase in side stiffness.
Particularly, when the tire cross-sectional height reaches a certain height, failures when run-flat traveling consist mainly of breakdowns in the vicinity of the rim cushion near the bead portion. Therefore, there is a strong demand for technology that prevents such failures and, simultaneously, ensures excellent riding comfort.
Conventionally, technology has been proposed to solve this problem wherein a cushioning rubber layer is disposed in the vicinity of a rim line on an outer side in a tire axial direction of a folded up portion of a carcass layer. When the side wall portion buckles, the cushioning rubber layer exerts a cushioning action, with respect to the upthrust by a rim flange, between the carcass folded up edge portion and the rim flange in order to prevent rupturing in that area (e.g. see Japanese Unexamined Patent Application Publication No. H07-304312A). Additionally, technology has been proposed wherein a folded up end of a carcass layer is distanced from a region where it contacts a rim flange top edge portion in order to suppress the generation and/or expansion of cracking due to the concentration of stress in the vicinity of the folded up end of the carcass layer (e.g. see Japanese Unexamined Patent Application Publication No. 2009-61866A).
However, when inflated air pressure declines, both of these proposals experience difficulty in suppressing the buckling of the tread portion and are limited as to effectiveness in enhancing run flat durability and, at the same time, do not directly lead to improvement effects in riding comfort when regular traveling. Therefore, neither proposal provides technology that can sufficiently satisfy the demands for both run flat durability and riding comfort.